1. Technical Field
The present invention relates to a vibrator element, a sensor unit, and an electronic device.
2. Related Art
There is widely used a vibration gyro sensor (hereinafter referred to as a vibration gyro) as an angular velocity sensor for enhancing the vehicle body control in vehicles, the vehicle localization of car navigation systems, and the vibration control correction function (so-called image stabilization) in digital cameras and digital video cameras, and so on. The vibration gyro is a device using a gyro vibrator element formed of a piezoelectric single-crystal substance such as quartz crystal as a high-modulus material and for detecting an electric signal as an angular velocity, the electric signal being generated in a part of the gyro vibrator element due to a vibration such as a tremor or a rotation of an object, and thus obtaining the displacement of the object by calculating the rotational angle.
As the vibrator element used for the gyro sensor, there is widely used a piezoelectric vibrator element (a gyro element) formed of a piezoelectric material such as quartz crystal (see, e.g., JP-A-5-256723 (Document 1)). The vibrator element described in Document 1 is a so-called tuning-fork piezoelectric vibrator element including a base section made of quartz crystal and a pair of vibrating arms extending from an end portion of the base section in parallel to each other. The primary surface (a first surface) of each of the vibrating arms is provided with a drive electrode (an excitation electrode) for supplying a drive voltage for exciting the vibrating arms, and a side surface perpendicular to the first surface is provided with a detection electrode. Further, by applying a drive signal (an excitation signal) to the drive electrode, the vibrating arms can be vibrated. Here, when applying the drive signal to the vibrator element to thereby cause a vibration (in-plane vibration) in a direction along the first surface in each of the vibrating arms, if the vibrator element is rotated taking an axis (e.g., the Y axis in the case of a gyro element having a quartz crystal Z plate as the substrate) in the extending direction of the vibrating arms as a detection axis, a vibration (out-of-plane vibration) in a direction perpendicular to the first surface is caused in the vibrating arms due to the Coriolis force. The amplitude of the out-of-plane vibration is proportional to the rotational speed of the vibrator element, and can therefore be detected as the angular velocity.
The base section and the vibrating arms of such a gyro element can integrally be formed by performing an etching process on a piezoelectric material such as quartz crystal using photolithography. Although the vibrating arms are originally designed to have a rectangular cross-sectional shape, the cross-sectional shape fails to be a rectangular shape, but exhibits a parallelogram or a rhombus, or a more complicated irregular form due to the etching anisotropy of the quartz crystal and the variation in the manufacturing process. In this case, if the cross-sectional shape of the vibrating arms is significantly different from the rectangular shape of the original design, the vibration direction of the vibrating arms is shifted from a design value to cause an unwanted vibration leakage called a leakage output, which is a factor of deteriorating the detection sensitivity of the gyro element. A gyro element having a cutting portion disposed in the vicinity of the root of the vibrating arms with respect to the base section as a measure for suppressing such a leakage output is introduced in, for example, JP-A-2008-209215 (Document 2).
The gyro element (angular velocity sensor element) of Document 2 has the base section and the vibrating arms extending from the base section, and the vibrating arms are provided with the drive electrodes for exciting the vibration in the width direction of the vibrating arms, and the detection electrodes (detecting electrodes) for detecting the charge due to the vertical vibration corresponding to the thickness direction of the vibrating arms. Further, a plurality of cutting portions formed by a laser process are disposed in at least one of end portions in the width direction of the vibrating arms in the vicinity of the root of the vibrating arms with respect to the base section. It is described that the leakage output (an oblique vibration) can be suppressed by varying the mass distribution using the cutting portions disposed in the vicinity of the root of the vibrating arms with respect to the base section.
However, in the gyro element described in Document 2, it is required to provide the extremely fine cutting portions in order for performing the fine adjustment for suppressing the leakage output, and there is a problem that it becomes more difficult to form the cutting portions in accordance with the miniaturization of the gyro element (the vibrator element) proceeding in recent years, and at the same time, the mechanical strength of the gyro element is degraded due to the formation of the cutting portions.